Steam drum baffle arrangement for a forced recirculation steam generator



United States Patent John M. Kovacik Portland;

Everett C. Hunt, Cape Elizabeth, Maine 824,798

May 15, 1969 Dec. 15, 1970 General Electric Company a corporation of New York Inventors Appl. No. Filed Patented Assignee STEAM DRUM RAFFLE ARRANGEMENT FOR A FORCED RECIRCULATION STEAM GENERATOR 7 Claims, 5 Drawing Figs.

U.S. CI 122/491,

55/444, 55/465 Int. Cl F22b 37/30 Field of Search 55/442,

[56] References Cited UNITED STATES PATENTS 2,648,397 8/1953 Ravese et al l22/488X 2,782,772 2/l957 Blaser l22/49lX Primary Examiner-Kenneth W. Sprague AttorneyWilliam C. Crutcher, Joseph B. Forman, Frank L.

Neuhauser and Oscar B. Waddell ABSTRACT: A steam drum for a forced recirculation steam generator with a number of evaporator return lines supplying a high velocity steam/water mixture to the upper portion of the drum. A baffle arrangement of perforate and imperforate plates reduces energy of the incoming mixture and supplies low velocity liquid to the lower part of the drum. An additional baffle controls the outgoing liquid flow.

PATENTEUBECISIBTB .3.'54T;0E5

' SHEEIIDFZ Ill-" 1 INVENTORS'.

JOHN M. KOVACIK', EVERETT c. HUNT,

THEIR ATTORNEY.

PATIENTEDUEBJISJIHYH" T 3.541.085 "siumanrz INVENTORSI JOHN M. KOVACIK, EVERETT C. HUNT,

THEIR ATTORNEY.

l STEAM DRUM BAFFLE ARRANGEMENT FOR A FORCED RECIRCULATION STEAM GENERATOR BACKGROUND OF THE INVENTION This invention relates to an improved baffle arrangement in a forced recirculation steam drum. 'A forced recirculation steam generator, is one wherein incomplete evaporation takes place inthe evaporator tubes and the resulting wet steam/water mixture is collected in a drum. The wet steam is drawn off from the drum and the liquid portion is returned again to the evaporator tubes, usually by a pump. The rate of steam generation may be expressed in terms such as pounds of steam per hour generated, but amuchhigher mass rate of flow passes between the drum and the evaporator tubes. This recirculated flow rate may be on the order of to l and is defined as the circulation ratio.

Itis desired to keep the steam drum as small as possible, yet a very large. volume of recirculating mixture of steam "and water is forced into the drum with high energy and velocity.

Also liquid is drawn from the bottom of the drum at a high fle arrangements for forced recirculation steam generators which reduce the'likelihood of carrying over water and impurities to the steam purifier.

DRAWING" These and many other objects of the invention will become apparent by reference to the'followingdescription, taken in connection with the accompanying drawing, in which:

FIG. '1 is a simplified schematicof aforced circulation steam generator, FIG. 2 is a transverse cross section of the steamdrum,

FIG. 3 is a longitudinal cutaway viewtaken along lines "FIGS. 4 and 5 are enlarged detail-cross sections of the upper baffle arrangement, taken along lines lV-IV and V-V respectively of FIG. 3.

SUMMARY or THE INVENTION Briefly stated, the invention is practiced by providing in the steam drum of a forcedrecirculation boiler, a baffle arrangement comprising imperforate plates receiving the high velocity steam/water mixture from the return lines, and two or more horizontal vertically spaced perforate plates which collect and distribute low velocity water uniformly to the bottom 7 i of the drum. An additional antiswirl baffle may be used to stabilizewater-flow from the bottom of the drum.

DESCRIPTION or THE INVENTION Referring to FIG. 1 of the drawing, a heat recovery steam generator includes a duct 1 carrying waste heat gases, such as from an industrial process or a gasturbine'. These gases may be additionally heated by supplementary firing in a burner (not shown). Inside duct 1 are horizontal tube banks comprising superheater tubes 2, evaporator tubes 3, and economizer tubes 4. Outside the ductis a steam drum 5. A high capacity circulating pump 6 is connected to receive liquid from the bottom of the drum 5 and supply it to. the header 7 to flow at a high rate in parallel through evaporator tubes 3, into header 8, and from there into a number of evaporator return pipes 9 spaced along the steam drum 5.

The drum is supplied with heated feedwater from the economizer through pipes 10, and saturated steam is drawn III-III of FIG. 2 showing detailsof the bafile and evaporator off at the top of drum 5 through line 11 to pass to the superheater. The rate of flow through return pipes 9 is on the order of five times as great as that through pipes 10, 1 1.

Referring to FIG. 2 of the drawing, the drum 5 includes a pressure shell 12, a liquid outlet 13 connected to the circulating pump, a feedwater inlet pipe 14, a saturated steam outlet pipe 15, and the aforementioned group of evaporator return lines 9 spaced axially along the pressure shell 12 at the upper part thereof. These discharge transversely into the shell above thenormal liquid level.

' 'Inside the upper portion of the drum is a steam purifier 16 which includes a screen mesh element 160 for coalescing particles and a separator element 16b of chevron baffle vanes. Entrained liquid droplets impinge and coalesce on the mesh 16a before passing into the separator, where the increased particle size improves the moisture separating effectiveness of the vaned elements. Liquidis collected in a lower chamber 16c and drains through line 16d.

Piping arrangements below the water level are indicated by reference numerals l7, 18. These are used for blow down to control the concentration of impurities and also to add chemicals for water treatment.

Disposed above the liquid outlet pipe 13 is an antiswirl baffle 19. It consists of two flat plates in a cruciform configuration centered above the outlet. A first plate 19a extends Ion gitudinally and is supported at either end by transverse angles 19b. A second transverse plate 19c is attached to 19a.

Referring now to the baffle arrangement in the upper righthand corner of FIG. 2, a vertical longitudinally extending plate '20 is attached to the inside of the pressure vessel and extends along in front of the outlets 9a of the return lines 9.

Extending between the pressure vessel wall and vertical plate 20 are two horizontal vertically spaced plates 21, 22. .These are of substantial construction and are perforated to provide about percent opening. As notes from FIG. 3, the perforated plates 21, 22 extend substantially the entire length of the drum. Transverse end plates 23 complete the baffle chamber enclosure. Thus the arrangement of perforate and imperforate plates l0.23 completely enclose a baffle chamber which serves to receive the high energy mixture of steam and water from the return lines 9.

Referring now to the detail view of FIG. 4, it will be seen that the perforate plates 21, 22 are'supported on angle members. A distribution plate 24 is employed below the outlet of each of the pipes 9 and is arranged horizontally to receive high velocity liquid which has previously impacted the vertical plate 20. Distribution plates 24 are axially spaced and serve to spread the flow longitudinally over the top perforate plate 21.

Referring to FIG. 5, which is a cross section taken between return lines 9, it can be seen that the perforate plates 21, 22 are staggered with respect to one another so that the holes are not in line. Thus there is no possibility of high velocity droplets passing through both plates without having their energy reduced.

The size and vertical spacing of the perforate baffles will vary somewhat with application. It has been found in a steam drum of the type shown, having a diameter as small as 3% to 4 0 feet and a length of 7 to 8 feet, suitable results have been obtained with baffles spaced about 4 inches apart. With such dimensions, a recirculating flow of greater than 500,000 pounds per hour has been achieved with steam generation of 120,000 pounds per hour at 600 p.s.i.g. with no significant carryover. In some designs, it may be desirable to have more than two spaced baffles, but two is deemed to be a minimum for effective results.

OPERATION The operation of the invention is as follows. The high velocity steam and water mixture from return lines 9 impacts against the imperforate plate 20 and, in the vicinity of the pipes, also against the imperforate distribution plates 24. The liquid is spread in both directions longitudinally and distributed over the top perforate plate 21 over. the length of the steam drum inside the baffle chamber. The liquid flows through the holes and is redistributed on the next horizontal perforate plate 22. From there the liquid drops into the bottom of the drum. Steam flows through the purifier 16 and out the saturated steam outlet 15. Any entrained particles are coalesced on mesh 16a and separated by vaned element 16b.

Liquid flows through the antiswirl baffle 19 and out the pipe 13 to the recirculating pump. The antiswirl baffle aids in water level control since it prevents a low water level over the outlet pipe which should otherwise be present due to a vortical swirl. Due to the effectiveness of the baffle chamber and the antiswirl baffle 19, liquid can be pumped through the evaporating tubes at a high circulation ratio without violent agitation of the water in the drum which would result in impurities or liquid being carried over into the steam outlet 15.

While the invention has been described herein in what is considered to be the preferred embodiment, other modifications will occur to those skilled in the art and it is intended to cover herein such modifications.

We claim:

1. In a forced recirculation steam generator, the combination of:

a steam drum comprising a horizontal annular pressure vessel with a normal liquid level and having a plurality of longitudinally spaced evaporator return conduits connected along an upper portion thereof and arranged to discharge a high velocity steam and water mixture transversely into the upper part of the pressure vessel above said liquid level, a baffle chamber enclosing said conduit outlets within the pressure vessel and comprising: an imperforate wall portion arranged to receive the high velocity mixture from said conduits;

a first perforate wall portion disposed to catch and dis tribute the mixture from said imperforate wall portion; and

a second perforate wall portion disposed below and vertically spaced from the first perforatewall portion and arranged to catch liquid flowing therethrough and to I redistribute it to the lower part of the pressure vessel.

2. The combination according to claim 1, further including a liquid outlet conduit in the bottom of the vessel and antiswirl bafile means mounted above said outlet conduit comprising plates arranged to reduce vortical swirl into said conduit.

3. The combination according to claim 1, including a steam separator disposed in said pressure vessel outside of said baffle chamber and a steam discharge conduit arranged to draw off steam from the upper portion of the pressure vessel through said separator.

4. The combination according to claim 1 including a feedwater supply conduit arranged to discharge liquid into the pressure vessel below said liquid level.

5. The combination according to claim 1, wherein said first and second perforate wall portions comprise a pair of horizontal plates each having uniformly spaced openings covering approximately 60 percent of the total plate area, the openings in one plate being offset with respect to the holes in the other plate.

6. The combination according to claim 1, wherein said imperforate wall portion includes a continuous vertical plate and a plurality of spaced horizontal distribution plates, said distribution plates being disposed below the discharge ends of said return conduits.

7. In a forced recirculation steam generator of the type having a steam drum, an evaporator, and means for circulating liquid from the drum to the evaporator and returning a steam/liquid mixture to the drum at a rate substantially in excess of steam generation, the improvement comprising:

a plurality of evaporator return conduits, connected along the drum and discharging above the normal water level;

a bafile chamber enclosing said conduit outlets within the drum, said chamber including a pair of horizontal, vertically spaced perforate plates disposed above the water level and arranged to distribute liquid to the lower part of the drum; and

an antiswirl baffle including plates disposed below the water level and arranged to reduce vortical swirl in liquid recirculated to said evaporator. 

